1. Field of the Invention
The present invention relates to system for controlling hydraulic systems and, in particular, concerns a system that moves to an initial position on start up in a smoother and safer manner.
2. Description of the Related Art
Hydraulic systems, such as elevators, platforms and gimbals are used in a wide variety of applications. In one particular application, such hydraulic control systems control the positioning of platforms used as sets in movie, television or other theater applications. In this application, a control system allows the operator to position a platform in a specific orientation. In some more complicated applications, a plurality of independent gimbals with associated actuators are used to provide 3 or even 4 degrees of motion of the platform. In this way, the specific orientation of the platform can be very specifically controlled.
The typical hydraulic system that is used to control gimbaled structures, platforms, elevators and the like generally include one or more hydraulic actuators, such as pistons that move the physical structure, one or more motion sensors that detects the location of the physical structure or piston during the motion and a control system that regulates the actuator so as to result in controlled movement of the structure. One difficulty that occurs with such hydraulic structures is that the actuators have a tendency to settle when the system is shut down. When the system is then restarted, the system may want to immediately move the structure to a desired starting location. However, if the system has settled significantly, this may result in sudden movements of the platform.
In applications where people or sensitive equipment may be positioned on the platform, such sudden movements can be dangerous. People or equipment can be dislodged from the platform. Further, such sudden movements may also result in the movement structure being stressed to the point where the system may be damaged. While this problem is very common in hydraulic based movement systems, it is a problem that can also occur with any movement system where sudden unpredictable movements may occur such as, for example, upon start up. Other systems where this problem may occur include systems that use electric linear or rotary actuators that utilize analog absolute position transducers.
From the foregoing, it will be appreciated that there is a need for a system that can safely move platforms, such as multi-axis hydraulic or electric servo systems, in circumstances where the platform may be subject to sudden unpredictable movement. To this end, there is a need for a system that can move a platform to a desired orientation in a controlled manner even when the system has settled from a desired orientation.